There is an ever increasing demand for wireless communication devices to perform a variety of applications. Some of those applications require substantial bandwidth. For example, next generation wireless communication systems may offer high speed downlink packet access (HSDPA) and high speed uplink packet access (HSUPA) to provide enhanced data rates over the radio interface to support Internet access and multimedia type applications.
The enhanced uplink concept currently being considered in the 3rd Generation Project Partnership (3GPP) intends to introduce substantially higher peak data rates over the radio interface in the uplink direction. Enhanced uplink data communications will likely employ fast scheduling and fast hybrid automatic repeat request (HARQ) with soft combining in the radio base station. Fast scheduling allows the radio base station to control when a wireless terminal is transmitting in the uplink direction and at what data transmission rate. Data transmission rate and transmission power are closely related, and scheduling can thus also be seen as a mechanism to vary the transmission power used by the mobile terminal for transmitting over an enhanced uplink channel. Neither the amount of uplink data to be transmitted nor the transmission power available in the mobile terminal at the time of transmission is known to the radio base station. As a result, the final selection of data rate will likely be performed in the mobile terminal. But the radio base station can set an upper limit on the data rate and/or transmission power that the mobile terminal may use to transmit over an enhanced uplink data channel.
Although the primary focus of enhanced uplink is on the radio interface performance and efficiency, the “bottleneck” may well occur further upstream from the radio interface in the transport of the uplink information between nodes in the radio access network (RAN). For example, the available uplink bit rate over the interface between a radio base station node in the RAN and a radio network controller node in the RAN (referred to as the Iub interface) may be a fraction of the available uplink bit rate over the radio interface. In this situation, high speed uplink packet access may overload the Iub interface between the radio base station and the radio network controller during peak bit rates. FIG. 1 illustrates that even though the downlink HSDPA bit rate over the radio interface is higher than the uplink HSUPA bit rate, the available bandwidth for high speed packet access data between the radio network controller and the radio base station is even less than the uplink HSUPA bit rate. The dashed line representing Iub High Speed Packet Access (HSPA) bandwidth limit is lower that the HSDPA and HSUPA bandwidths.
Consider the following simple example. A radio base station (sometimes referred to as a “Node B” using 3GPP terminology) controls three cells that have an enhanced uplink data transmission capability. Assume that the radio base station is connected to a radio network controller using one 4 Mbps link to support the enhanced uplink data transmitted from the radio base station and the radio network controller. Assume that the enhanced uplink capability may be up to 4 Mbps per cell. In this situation, enhanced uplink communication data from three cells at or near capacity cannot be transported from the radio base station to the radio network controller over the single 4 Mbps link. The result is a congested or overload situation. This congestion could result in long delays and loss of data, which reduces quality of service.
One possible solution to avoid this kind of overload situation would be to “over provision” the bandwidth resources in the radio access network for communications between radio network controllers and radio base stations. But this is inefficient, costly, and in some existing mobile communications networks, not practical. For high speed downlink, an HSDPA flow control algorithm could be employed by the radio base station to reduce the available downlink HSDPA bit rate to a level that suits the Iub interface bandwidth. But this control methodology cannot be employed in the opposite uplink direction because, as explained above, the amount of uplink data to be transmitted from mobile terminals is not known to the radio base station. Should the uplink enhanced bit rate over the radio interface significantly exceed the Iub uplink bandwidth, congestion will likely occur with long delays and possibly lost or otherwise corrupted data frames. What is needed, therefore, is a way to detect and then control an overload or other congested situation in the radio access network as a result of uplink mobile terminal communications being transported between nodes in the radio access network.
The technology described herein meets this need as well as other needs. Congestion associated with transporting in the RAN uplink information originating from one or more mobile terminals is detected. That detected congestion is then reduced using any suitable technique(s) and may be implemented in one or more nodes in the RAN. One advantageous (but non-limiting) application is to a RAN that supports high speed uplink packet access (HSUPA) and/or one or more enhanced uplink dedicated channels (E-DCHs). Uplink congestion may be detected over an interface between a radio network controller and a radio base station (the Iub interface) and/or an interface between radio network controllers (the Iur interface).
Although congestion reduction may be performed in any suitable fashion, one example approach is to reduce a parameter associated with a bit rate at which uplink mobile terminal information is transported through the RAN. For example, where the uplink mobile terminal information is communicated using uplink data flows, the bit rate parameter may be reduced by reducing a bit rate of one or more uplink data flows. It may be appropriate to limit the bit rate of the one or more uplink data flows actually causing the congestion in the RAN; alternatively, the bit rate of one or more lower priority uplink data flows may be reduced.
There are a number of different ways that the bit rate parameter may be reduced. For example, a bit rate parameter value may correspond to an absolute bit rate parameter value or a relative bit rate parameter value sent to one or more mobile terminals, e.g., a maximum bit rate or transmission power or a percentage or fraction of a current bit rate or transmission power. Another approach is to reduce the bit rate parameter using a capacity limitation message. If the RNC detects a congested condition in the RAN, it can send a capacity limitation to a radio base station, which then schedules uplink transmissions from mobile terminals to effect that capacity limitation, e.g., by using scheduling grants or credits.
In some situations, more drastic measures may be necessary to reduce the bit rate parameter such as dropping one or more frames of one or more uplink mobile terminal communications. In soft/softer handover situations, one or more of the diversity handover links may be released to reduce the bit rate parameter. Another technique employs sending negative acknowledgment messages for received packets back to the mobile terminal causing the mobile terminal to retransmit those negatively acknowledged packets. This effectively reduces the uplink bit rate through the RAN.
The congestion control may be implemented by sending control information either over a separate control signaling channel or in a user data plane where the control signaling is sent along with the data over a data channel.